1. Field of the Invention
The present invention relates to a technology of embedding a plurality of types of information with different degrees of importance in image information.
2. Description of the Related Art
In recent years, electronic watermarking technology has been developed in which information for preventing tampering and copying is embedded in image data and document data. Also, several technologies have been suggested in which the electronic watermarking technology is applied for embedment in a document output as a paper medium in a format that is not visually noticeable by the user.
For example, Japanese Patent Application Laid-Open No. 2003-101762 suggests a technology of embedding secret information by disposing dot patterns.
With the use of such a technology, it is possible to embed in a paper document security information for preventing forgery and tampering on a print document, electronic information representing the contents written in a print document, Uniform Resource Locator (URL) information indicative of a web site for guiding the contents regarding the print document, and others. With this, a new added value can be provided to a print document.
Meanwhile, as a technology of adding some information to the background of a paper document in a manner similar to the above, a technology of adding tint blocks has been known. In this technology, the limit of the image reproduction capability of an image processing apparatus is used to cause some character or the like to appear when a paper document is copied.
For example, Japanese Patent Application Laid-Open No. 2005-094326 suggests a technology of generating a tint block image at high speed in a memory-saving manner and then superposing the tint block image on the background of a document.
As disclosed in Japanese Patent Application Laid-Open No. 2005-094326, the background portion is written with fine dots or the line exceeding the limit of the image representation capability is lost at the time of copying. That is, even if a large amount of information is written, a dot size that allows copying (that is, copy-tolerant dot size) has a limitation.
In the technology disclosed in Japanese Patent Application Laid-Open No. 2003-101762, however, if a large amount of information is embedded with copy tolerance, a large amount of dots of a predetermined size are added, thereby posing a problem that the appearance of the printed print document is deteriorated.